1. Field of the Invention
This invention relates generally to pumps, and more particularly to a pump well adapted for use in an inking mechanism of the offset printing press, among other applications. Still more particularly, the invention pertains to a pump of the kind having a piston or plunger slidably received in a bore in a pump housing for joint rotation and linear reciprocation, featuring provisions for making the pump as constant as feasible in the rate of ink or other fluid delivery therefrom.
2. Description of the Prior Art
The inking pump of the kind in question differs from the so-called piston pump or reciprocating pump in that the plunger not only reciprocates linearly but rotates, too, at the same time. This type of pump is per se not new, however. Japanese Patents Nos. 2,864,447 and 3,095,744 are hereby cited as teaching pumps with a reciprocating and rotating plunger. Both of these prior art pumps are alike in requiring two plunger strokes and one revolution to complete a cycle; that is, the fluid is drawn in while the plunger is both traveling linearly in one direction and rotating a half revolution, and forced out while the plunger is both traveling linearly in the other direction and rotating another half revolution.
An objection to these known pumps, particularly in their use as inking pumps in an offset printing press, is that the suction stroke and discharge stroke of the plunger alternate, resulting in intermittent ink discharge. The ink density of the image is the highest at the end of the discharge stroke, diminishes during the ensuing suction stroke, and restarts rising upon commencement of the next discharge stroke. Such cyclic change in ink density presents a bar to the production of high-quality printings. Even totally defective printings may occur depending upon the images being printed, for some such images may be printed densely, and others thinly, to an unacceptable degree.
The present seeks to make a pump of the kind defined, far more constant than heretofore in the rate of fluid delivery during each cycle of operation and hence, in its intended typical use as an inking pump in an offset printing press, to enable the latter to produce printings of unfluctuating ink density.
Briefly, the present invention may be summarized as a pump suitable for use in an inking mechanism of a printing press, among other applications. Included is a plunger received in a bore in housing means for both angular and linear motion relative to the same, defining a first and a second opposed fluid chamber in the bore. The housing means has formed therein a first and a second suction port with a spacing therebetween axially of the bore, and a first and a second discharge port with a spacing therebetween axially of the bore, there being a preassigned angular spacing about the axis of the bore between the first and second suction ports and the first and second discharge ports, all of the first and second suction ports and the first and second discharge ports being open to the bore. The plunger has formed therein a first recess adjacent a first end thereof and in a first preassigned angular position thereon for placing the first fluid chamber in successive communication with the first suction port and the first discharge port during each complete revolution of the plunger, and a second recess adjacent a second end thereof and in a second preassigned angular position thereon for placing the second fluid chamber in successive communication with the second suction port and the second discharge port during each complete revolution of the plunger.
The plunger is driven for joint angular and linear travel relative to the housing means, making one complete linear reciprocation (i.e. one to-and-fro travel) during each complete revolution, or turning half a revolution during each stroke. During plunger travel from the first toward the second fluid chamber, the fluid will be drawn from the first suction port into the first fluid chamber via the first recess in the plunger and, at the same time, delivered from the second discharge port by being forced out of the second fluid chamber via the second recess in the plunger. During the return stroke of the plunger from the second toward the first fluid chamber, the fluid will be drawn from the second suction port into the second fluid chamber via the second recess in the plunger and, at the same time, delivered from the first discharge port by being forced out of the first fluid chamber via the first recess in the plunger.
Thus the pump draws in the fluid twice, and forces it out twice, during each cycle of operation. Therefore, through appropriate determination of the relative sizes and locations of the suction and discharge ports and the plunger recesses, fluid delivery will continue at all times but when the plunger is at its xe2x80x9cdead centerxe2x80x9d positions at both extremities of its stroke.
Constructed and operating as briefly outlined in the foregoing, the pump according to the present invention is particularly well suited for use in an inking mechanism of an offset printing press, in which application a plurality or multiplicity of pumps, each configured according to the invention, may be juxtaposed for conjoint operation in conformity with the usual practice in the art. The inking pump arrangement according to the invention will cause no such fluctuations in the ink density of the printings as have been conventionally experienced. No overly dense or overly light printings will be produced either, as the pumps are readily adjustable for optimum ink density according to the images being printed, making possible the printing of products that meet the most stringent demands of the clients.
The above and other objects, features and advantages of this invention and the manner of realizing them will become more apparent, and the invention itself will best be understood, from a study of the following description and appended claims, with reference had to the attached drawings showing the preferred embodiment of the invention.